The present invention relates to the lighting arts. It especially relates to a rugged solid-state plane wave light source for producing a substantially plane wave light beam that is suitable for vehicle headlights and other applications, and will be described with particular reference thereto. However, the invention will also provide solid-state light sources producing other types of light distributions, such as light that is focused in one dimension and planar in an orthogonal dimension, plane wave light that is angularly tilted, and the like, for use in downlighting and other applications throughout the lighting arts.
Present vehicular headlights typically employ filament-based light sources such as halogen lamps, or high-intensity discharge lamps that produce electric arc illumination by electrical discharge between electrodes in a high-pressure gas ambient. Such light sources produce a generally point source of light, which is collected and directed by optics typically including a back-reflector and front lens. The optics preferably produce a beam that is forwardly directed in front of the vehicle, and a diameter or size of the back-reflector and front lens controls the headlight beam size.
In the United States, vehicles typically have both high-beam and low-beam headlights, the former being used on substantially empty country roads and highways to provide maximum forward illumination, and the latter being used in cities or other populated roadways. The low-beam headlights are a compromise between providing forward illumination for the driver and avoiding glare and possible blinding of oncoming traffic by the vehicle headlights. The low-beam headlights are designed and mounted on the vehicle in a manner which concentrates the low-beams below the horizontal, i.e. onto the road rather than toward oncoming traffic. The low-beams are also preferably used in snowy, rainy, or foggy driving conditions to reduce back-scattered headlight illumination which can blind the driver.
Existing headlights have certain disadvantages. They are large, particularly in the vertical direction, which degrades aerodynamic performance and aesthetic qualities of vehicles. Vehicle designers are further constrained because two separate sets of headlights for the low-beams and the high-beams are typically used to provide both illumination modes.
In response to these aerodynamic and aesthetic styling issues, vehicle headlights are usually custom-designed for a particular vehicle model and make. This increases headlight cost. Some vehicles use “sealed beam” headlights in which the halogen or discharge lamp, the back-reflector, and the forward lens are integrated into a single hermetically sealed unit. When a sealed beam headlight fails for any reason, the entire sealed beam unit must be replaced. Alternatively, some vehicles use a headlight housing including the back-reflector and the forward lens, and a separate halogen or discharge lamp that inserts into a receptacle of the back-reflector. These headlights permit replacement of the failed lamp without replacing the optics, but increase a likelihood of headlight misalignment due to the additional detachable lamp connection.
Another disadvantage of incandescent halogen or discharge lamps is limited reliability and a catastrophic failure mode. The wire filaments of incandescent light sources are fragile, and halogen headlights in particular are typically short-lived. Discharge lamps include high-pressure gas contained in a transparent glass or plastic bulb, and can present shatter hazards. Moreover, both incandescent and discharge lamps employ a single light source which is shaped into a beam by optics. Hence, failure of the light source, for example by breakage of the incandescent filament or leakage of the high-pressure discharge gas, results in complete failure of the headlight, which creates a driving safety hazard.
The present invention contemplates an improved apparatus and method that overcomes the above-mentioned limitations and others.